1. Field of the Invention
This invention relates to power safety devices, and in particular to a safety device permitting shutdown of the power to an educational laboratory or other environment in which potentially dangerous equipment is present.
2. Description of the Prior Art
In an educational laboratory, such as those containing woodworking and metalworking equipment, it is common to have machines, such as drills, lathes, and other apparatus, for performing cutting and forming operations. When these machines are operated by skilled operators, the chances of danger are relatively small. However, in an educational environment, these machines are often operated by inexperienced students or those unfamiliar with the workings of the machines, and the possibility of injury resulting from operation of the machines is greatly increased.
When confronted with an adverse situation, students usually will react in a predicable manner. Hopefully, with proper instruction, the student defines the problem and reacts with the appropriate solution. In some cases, the student will panic and react with an inappropriate response, making the situation more dangerous, or will just "freeze" and do nothing at all.
An instructor is usually present in the laboratory to supervise the operation of these machines, but it is impossible for the instructor to be present at the position of each machine in the laboratory, particularly if the laboratory is relatively large. When such an emergency situation occurs, it is important that the instructor intervene to prevent any injury or any further injury to the students in the laboratory. It is most important for the instructor to immediately stop the operation of the machine as an initial step in this intervention. For this reason, most educational laboratories in secondary and post-secondary schools are equipped with some form of master power shutdown system. Normally, this system takes the form of "panic buttons" mounted around the outside walls of the laboratory. These panic buttons are spaced around the laboratory to enable the instructor or some other individual to shut off the power within the laboratory in the event of an emergency, and thus shut down the potentially dangerous machinery in the laboratory.
The panic button operates a power shutdown system connected to the master power supply system for the laboratory. Two types of shutdown units are commonly used. In larger shops with higher power requirements, a relay system is employed which is designed around primary contactors held closed by a magnet. When the circuit is interrupted by actuation of the panic button, the electric magnet deactivates, and a spring pulls the contactors out, interrupting the main power source. Smaller laboratories and shops employ a system which is designed around contactors activated by a holding circuit. When the button is depressed, a circuit is completed, energizing the magnet.
The placement of the panic buttons around the walls of the laboratory is critical, particularly in a larger laboratory in which the instructor must have access to a panic button within seconds. It is necessary, therefore, for the instructor to know the location of the panic buttons in all of the laboratories and be able to react within an extremely short period of time in the case of an emergency. In larger laboratories in which a large number of panic buttons are present, it is possible for the instructor to become momentarily confused or require additional time to locate the panic button in an emergency situation. Reaction to an emergency situation appears to be one of the major drawbacks of the panic button system. The time required for someone to react to an adverse situation, locate a panic button, and then push this button is in many instances too long.